Excitation and emission processes of Tb in porous anodic alumina

The strong photoluminescence (PL) of porous anodic alumina (PAA) with terbium deposition is reported. PAA, which has a regular pore morphology, is considered an effective template for fabricating luminescent composites. Tb was deposited onto PAA films by immersion in alcoholic solution with terbium chloride followed by heat treatment. The PL spectra demonstrate typical bands of Tb³⁺ corresponding to ⁵D₄ → ⁷F_j (j = 3, 4, 5, 6,) electron transition, with the maximum at 18,360 cm⁻¹ (⁵D₄ → ⁷F₅). The PL mechanism of Tb³⁺ was systematically studied with annealing temperature. The non-radiative relaxation channel is provided by OH hydroxyls at the surface of porous anodic alumina and, after annealing at 900 °C, the PL yield is highly improved. The PL intensity of Tb³⁺ increases with laser power and a saturation phenomenon, associated with the ratio of Tb³⁺ to Tb⁴⁺ ions, is observed at approximately 90 W/cm². Based on a theoretical model, the optical cross-section σ of terbium in PAA is estimated, with a value close to that of other porous materials doped with the rare-earth elements.     

使用光栅单色仪测量红宝石晶体的吸收和发射光谱

使用WDS-8型光栅单色仪测量了室温下红宝石晶体的吸收光谱和发射光谱.通过该实验,学生在了解光致发光原理及光致发光材料光谱特性的同时,掌握单色仪的使用方法和技巧.     

Magnetic field dependence of red emission intensity of ruby at various temperatures

Application of a magnetic field perpendicular to the c-axis of a thin slice of pink ruby at low temperatures reduces the intensity of R-line and vibronic emission. At field intensity H = 6 kG the loss of vibronic emission exceeds 10%. The decay time decreases by a similar fraction. The method used for studying intensity involves on-off modulation of the field, and digital integration. A function which describes the observed fractional reduction of intensity is $\text{F(H) =}\text{AH}{}^2\text{(1 + BH}{}^2\text{)}$ where A and B are nearly constant below 77 K, but decrease rapidly between 100 K and 200 K. The function can be derived by assuming that radiationless transitions to the ground state occur with probability proportional to H² from low-lying vibronic states of ²E. Thermal excitation from these states to states in the neighborhood of ²T₁ is proposed as the mechanism for quenching the magnetic field effects.     

Photon emission under bombardment of ruby by ions and electrons of medium energies

The characteristics of optical radiation produced under bombardment by ions (1–15 keV) and electrons (100–1000 eV) of a ruby surface are studied. Two broad bands with maxima at 330 and 450 nm attributed to defects of the crystal lattice are discovered in the spectral region of 200 to 800 nm. Characteristic radiation related to radiative relaxation of excited Cr³⁺ ions in the near-surface region of the crystal is observed. The dependence of the radiation intensity on the energy and current density of the bombarding particles is obtained experimentally. The degree of radiation polarization is determined.     

Increasing the directionality of ruby laser emission by adjustment of the external reflectors

It is shown that by increasing the distance between the external mirrors of a ruby laser it is possible to reduce the angle of divergence of the radiation at the expense of energy alone. There is an optimal distance at which the light sum of the axial luminous intensity is maximum.     

Role of pure dephasing in the broadening of zero-phonon emission lines in ruby

A theoretical analysis is made of the homogeneous linewidth of the electronic Raman transition between ē and 2ā excited states of Cr³⁺ observed in optically pumped ruby, in comparison with the widths of the phosphorescence R₁ and R₂ lines. In particular, we consider the phenomenological correlation between the broadening processes of the ē and 2ā levels, implied by the experimental fact that the magnitude of the Raman linewidth is approximately equal to the average, rather than the sum, of the R₁ and R₂ linewidths. The origin of this correlation is shown to be the quenching of pure-dephasing processes, associated with elastic phonon scattering, of the ē ? 2ā transition, while the pure-dephasing rates of the phosphorescence transitions are comparable to the rates of population-relaxation (lifetime-broadening) processes, associated with inelastic phonon scattering.     

Excitation and emission of metal electrons in atom-surface collisions

Electron-hole pair excitation and ionization probabilities are calculated for atomic collisions with metal surfaces at high incident energies. The method adopted is based on a Sudden Collision Approximation, and a realistic model is employed for the bound and continuum electronic states involved. The parameters used in the calculations are for Ar, He, H atoms impinging on a Li surface at 300 eV. The main results are: (1) Only single electron-hole pair excitations are important; multiple pair contributions are small. (2) The transitions are dominated by the behavior of the electronic wavefunctions in the tunneling region and may serve as a probe of this regime. (3) The excitation efficiency is in the order H ? Ar ? He, the effectiveness of hydrogen being due to its stronger, longer-range coupling. (4) The maximum excitation probabilities are for electrons ejected with relatively low excess energies. (5) Total transition probabilities are about 0.5 per collision for H, and about 0.1 for Ar, indicating that these are important, easily detectable processes. Experiments in this field should provide important information on electronic wavefunctions at the metal-gas interface, and on gas-metal interactions at high energies.     

Lepton-hadron processes beyond leading order in quantum chromodynamics

We present a summary of QCD formulae describing the effects of scaling violation in leptonhadron processes, with the inclusion of recently derived higher order corrections. Deep inelastic leptoproduction, one-hadron inclusive distributions in leptoproduction and ine ⁺ e ^? annihilation and Drell-Yan processes are discussed in detail. Higher order corrections to parton densities, fragmentation functions and to lepton-parton cross-sections in the above processes are presented in a common factorization scheme, so that a comparative analysis of various processes as well as an independent analysis of each of them is possible. A discussion of the various scheme dependences at next-to-leading level is also included.     

Surface damage to ruby laser crystals

Surface damage to ruby laser crystals is investigated. To identify the surfacedamage mechanism, the dependence of the damage threshold on the laser pulse duration is investigated from 300 nsec to 0.4 msec. From this dependence, as well as from the dependence of the damage threshold on the defect content of the surface layer, it is concluded that the damage to the surface of the mechanically worked laser ruby crystals is due to a thermal mechanism. Methods are developed for obtaining, by thermal evaporation of oriented crystals, surfaces with increased endurance to laser damage. Such surfaces have a low light-scattering stability.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 101, pp. 9–30, 1978.     

Surface model for field emission processes

The processes of field electron emission from solids and field ion production at surfaces are well understood for plane emitting surfaces. The actual surfaces are not plane on an atomic scale and it is worthwhile to develop a way to treat deviations from a flat surface quantitatively, at least to some extent. In this paper the model of a hemispherical projection on a plane surface is set up, as an approximation to the way that an atom projects from the background of a crystalline surface. It is expected that the model will be valuable in analyzing various field emission processes. Application is made to the resolving power of the field ion microscope.